The invention concerns a mold for molding a tire, said mold containing at least one molding element designed to mold a cut in said tire; this invention also concerns a molding element designed to mold a cut in a tire.
In order to mold a cut in a tire tread, a mold made up of a plurality of mold members is ordinarily used, each of said members being able to contain a plurality of molding elements projecting on the molding surface of said mold members. The term "cut" is understood to embrace grooves (at least 3 mm wide) as well as incisions (that is, grooves less than 3 mm wide).
A molding element generally contains two parts: a first part forming the molding part of the molding element projects on the molding surface of the mold, and a second part situated in the extension of the first is anchored in the mold. The anchorage of said second part is, for example, for a mold made by casting, obtained at the time of casting of the material constituting said mold, said material trapping said second part of the molding element during the phase of cooling of said material.
During molding and vulcanization of the tire, the molding part of the molding element is sunk inside the rubbery material constituting the tire in order to form a cut. After vulcanization of the tire, the components of the mold are moved in their proper mold stripping direction and gradually separate from one another so as to release the molded tire by carrying the mold elements along with them to extract them from the tire.
Producing a tire having durable rolling performances can be accomplished by the use of incisions, the geometry and/or mean orientation of which appreciably evolve(s) with wear of the tire tread. However, when such incisions are molded, usually by means of rigid molding elements, the mold stripping of said elements is sometimes very difficult (for it necessitates a force that increases with the number of molding elements of this type), and is even impossible without risking damage to the tire (by tearing away rubber compound parts).
For example, French Application 2,722,145 discloses a tread containing a plurality of elements in relief, some of them being provided with incisions, whose mean direction on the rolling surface gradually changes with the wear of said tread. As soon as the change of orientation becomes great, it is clear that obtaining such an incision by means of a molding element containing a rigid wire forming the molding part of the same geometry is difficult, at least in the mold stripping phase (that is, of extraction of said molding element). The term "wire" is understood to embrace blades.
The same is true when a molding element contains at least one rigid wire having a helical or twisted shape or any geometry entailing the existence of a torque resulting from torsion being exerted on the molding part during mold stripping. In order not to damage the appearance of the tread during said mold stripping operation, the use of this type of element necessitates particular precautions usually incompatible with the demands of industrial production.